Search for an exotic decay of the Higgs boson to a pair of light pseudoscalars in the final state with two b quarks and two τ leptons in proton–proton collisions at sqrt(s)=13TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Search

for

an

exotic

decay

of

the

Higgs

boson

to

a

pair

of

light

pseudoscalars

in

the

final

state

with

two

b quarks

and

two

τ

leptons

in

proton–proton

collisions

at

√

s

=

13

TeV

.

The

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory:

Received25May2018

Receivedinrevisedform16July2018 Accepted7August2018

Availableonline31August2018 Editor:M.Doser Keywords: CMS Physics Higgsboson Exoticdecays NMSSM 2HDM+S

A search for an exotic decay of the Higgs boson to a pair of light pseudoscalar bosons is performed for the first time in the final state with two b quarks and two

τ

leptons. The search is motivated in the context of models of physics beyond the standard model (SM), such as two Higgs doublet models extended with a complex scalar singlet (2HDM+S), which include the next-to-minimal supersymmetric SM (NMSSM). The results are based on a data set of proton–proton collisions corresponding to an integrated luminosity of 35.9 fb−1, accumulated by the CMS experiment at the LHC in 2016 at a center-of-mass energy of 13 TeV. Masses of the pseudoscalar boson between 15 and 60 GeV are probed, and no excess of events above the SM expectation is observed. Upper limits between 3 and 12% are set on the branching fraction

B(h →aa→2

τ

2b)assuming the SM production of the Higgs boson. Upper limits are also set on the branching fraction of the Higgs boson to two light pseudoscalar bosons in different 2HDM+S scenarios. Assuming the SM production cross section for the Higgs boson, the upper limit on this quantity is as low as 20% for a mass of the pseudoscalar of 40 GeV in the NMSSM.

©2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3_.

1. Introduction

Within the standard model (SM), the Brout–Englert–Higgs mechanism[1–6] isresponsible forelectroweaksymmetry break-ingandpredictstheexistenceofascalarparticle—theHiggsboson. AparticlecompatiblewiththeHiggsbosonwasdiscoveredbythe ATLAS and CMScollaborations at the CERN LHC [7–9]. Measure-mentsofthe couplingsandpropertiesofthisparticleleave room forexoticdecaysto beyond-the-SMparticles,witha limit of34% onthisbranchingfractionat95%confidencelevel(CL),usingdata collectedatcenter-of-massenergiesof7and8TeV [10].

The possible existence of exotic decays of the Higgsboson is well motivated [11–16]. The decay width of the Higgs boson in the SM isso narrow that a smallcoupling to a light state could lead tobranching fractionsof theHiggs bosonto that light state oftheorderofseveralpercent.Additionally,the scalarsectorcan theoretically serve as a portal that allows matter froma hidden sectortointeractwithSM particles [17].Ingeneral, exoticdecays oftheHiggsbosonareallowedinmanymodelsthatareconsistent withallLHCmeasurementspublishedsofar.

 _{E-mailaddress:cms-publication-committee-chair@cern.ch.}

An interesting class of such processes consists ofdecays to a pair oflight pseudoscalar particles,which then decayto pairs of SM particles. This type of process is allowed in various models, includingtwoHiggsdoubletmodelsaugmentedbyascalarsinglet (2HDM

+

S). Sevenscalarandpseudoscalarparticlesarepredicted in 2HDM

+

S. Oneofthem, h, isa scalarthat canbe compatible withthediscoveredparticlewithamassof125GeV,andanother, thepseudoscalara,canbelightenoughsothath

→

aa decaysare allowed.

Fourtypesof2HDM,andbyextension2HDM

+

S,forbid flavor-changing neutralcurrentsattreelevel [18].Intype I,all SM par-ticlescoupletothefirstdoublet.Intype II,up-typequarkscouple to the firstdoublet, whereas leptons anddown-type quarks cou-ple to the second doublet. The next-to-minimal supersymmetric SM (NMSSM) is a particular case of 2HDM

+

S of type II that brings asolution to the

μ

problem [19]. In type III, quarks cou-ple tothefirstdoublet,andleptons tothesecond one.Finally,in type IV, leptons and up-type quarks couple to the first doublet, while down-typequarks couple to the second doublet [15]. The branching fractionsofthe lightpseudoscalars topairsofSM par-ticlesdependonthetypeof2HDM

+

S,onthepseudoscalarmass ma,andon tan

β

,definedastheratioofthevacuumexpectation

values ofthesecond andfirst doublets. Thevalue ofthe

branch-https://doi.org/10.1016/j.physletb.2018.08.057

0370-2693/©2018TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

Fig. 1. Predicted B(aa

→

bbτ τ) for ma=40GeV in the different models of 2HDM+S,asafunctionoftanβ.Thepictureisessentiallythesameforallma hy-pothesesconsideredinthisLetter.Thebranchingfractionsarecomputedfollowing theformulasofRef. [15].

ingfraction

B(

aa

→

bbτ τ

)

isslightlyabove10%intheNMSSM—or moregenerallyin2HDM

+

S type II—fortan

β >

1,andcanreach uptoabout50%in2HDM

+

Stype IIIwithtan

β

∼

2,asshownin Fig.1.

SeveralsearchesforexoticdecaysoftheHiggsbosontoapair oflight short-lived pseudoscalar bosons havebeen performedby the CMS Collaboration with data collected at a center-of-mass energy of 8TeV in different final states: 2μ2b for 25

.

0

<

ma

<

62

.

5GeV [20], 2μ2τ for 15

.

0

<

ma

<

62

.

5GeV [20], 4τ for 4

<

ma

<

8GeV [21] and 5

<

ma

<

15GeV [20], and 4μ for 0

.

25

<

ma

<

3

.

50GeV [22].TheCMSCollaborationalsostudiedthe2μ2τ

finalstatefor15

.

0

<

ma

<

62

.

5GeV at acenter-of-massenergyof

13TeV [23]. The ATLASCollaboration reportedresultsforthe fol-lowingfinalstatesatacenter-of-massenergyof8TeV:4μ,4e,and 2e2μ for15

<

ma

<

60GeV [24]; 4γ for 10

<

ma

<

62GeV [25];

and2μ2τ for 3

.

7

<

ma

<

50

.

0GeV [26]. At a center-of-mass

en-ergyof 13TeV, theATLAS Collaboration published results forthe 4b decaychannelfor20

<

ma

<

60GeV [27],and4μ,4e,and2e2μ

for 1

<

ma

<

60GeV [28]. The 2b2τ final state has never been

probedso far. Thisfinal state benefits fromlarge branching frac-tionsinmostmodelsbecauseofthelargemassesof

τ

leptonsand b quarkswithrespect toother leptons andquarks.The presence oflightleptons originatingfromthe

τ

decaysallowseventstobe triggeredinthedominantgluonfusionproductionmode.

ThisLetterreportsonthefirstsearchwiththeCMSexperiment forexoticdecaysoftheHiggsbosontoapairoflightpseudoscalar bosons,inthefinalstatewithtwo

τ

leptonsandtwob quarks.The searchfocusesonthemassrangebetween15and60GeV.Forlow mavalues,betweenthebb thresholdand15GeV,thedecay

prod-uctsofeachofthepseudoscalarbosonsbecomecollimated,which wouldnecessitatetheuseofspecialreconstructiontechniques.

The search is based on proton–proton(pp) collision data col-lectedata center-of-massenergyof13TeV andcorresponding to an integratedluminosity of35

.

9fb−1. ThroughoutthisLetter, the term

τ

h denotes

τ

leptons decaying hadronically. The

τ τ

final

statesstudiedinthissearchareeμ,eτh,and

μτ

h.Despiteitslarge

branchingfraction, the

τ

h

τ

h final state isnot considered because

thesignalacceptanceisnegligiblewiththetransverse momentum (pT) thresholdsavailableforthe

τ

h

τ

h triggers.The ee and

μμ

fi-nalstatesforthe

τ τ

pairare notconsidered either,becausethey havealowbranchingfractionandsufferfromalargecontribution ofDrell–Yanbackgroundevents.

2. TheCMSdetector

The central feature of the CMS apparatus is a superconduct-ingsolenoidof6m internaldiameter,providingamagneticfieldof 3

.

8T. Within the solenoid volume, there are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorime-ter (ECAL), and a brass and scintillator hadron calorimeter, each composedofabarrelandtwoendcapsections.Forward calorime-ters extend the pseudorapidity coverage provided by the barrel andendcapdetectors.Muonsaredetectedingas-ionization cham-bersembeddedinthesteelflux-returnyokeoutsidethesolenoid. Events of interest are selected using a two-tiered trigger sys-tem [29].A moredetaileddescriptionoftheCMSdetector,together witha definitionofthe coordinatesystemused andtherelevant kinematicvariables,canbefoundinRef. [30].

3. Simulatedsamplesandeventreconstruction

Thesignalandsomeofthebackgroundprocessesaremodeled withsamplesofsimulatedevents.The MadGraph5_amc@nlo [31] 2.3.2 generator isused fortheh

→

aa

→

2τ2b signalprocess, in gluonfusion(ggh),vectorbosonfusion(VBF),orassociatedvector boson(Wh,Zh)processes.Thesesamplesaresimulatedatleading order (LO) inperturbative quantumchromodynamics (QCD) with theMLMjetmatchingandmerging [32].TheZ

+

jets andW

+

jets processesarealsogeneratedwiththe MadGraph5_amc@nlo gen-eratoratLOwiththeMLMjetmatchingandmerging.TheZ

+

jets simulation contains non-resonant Drell–Yan production, with a minimum dilepton mass threshold of 10GeV. The FxFx merging scheme [33] is used to generate diboson background with the MadGraph5_amc@nlo generator at next-to-LO (NLO). The tt and singletopquarkprocessesaregeneratedatNLOwiththe powheg 2.0 and 1.0 generator [34–39]. Backgrounds from SM Higgs bo-son production are generatedat NLO withthe powheg 2.0 gen-erator [40], and the minlohvj [41] extension of powheg 2.0 is used for the Wh and Zh simulated samples. The generators are interfaced with pythia 8.212 [42] to model the parton shower-ingandfragmentation,aswell asthedecayofthe

τ

leptons.The CUETP8M1tune [43] is chosenforthe pythia parametersthat af-fectthedescriptionoftheunderlyingevent.Thesetofparton dis-tributionfunctions(PDFs)isNLO NNPDF3.0forNLOsamples,and LO NNPDF3.0 for LO samples [44]. The full next-to-NLO (NNLO) plus next-to-next-to-leading logarithmic (NNLL) order calculation [45–50], performed withthe Top++ 2.0 program [51], is used to compute a tt production cross section equal to 832+₋20₂₉(scale)

±

35

(

PDF

+

α

S

)

pb setting the top quark mass to 172

.

5GeV. This

cross section is used to normalize the tt background simulated with powheg.

All simulated samples includeadditional proton–proton inter-actions per bunch crossing, referred to as “pileup”, obtained by generatingconcurrentminimumbiascollisioneventsusing pythia. The simulated events are reweighted insuch a way to have the same pileupdistribution asdata.Generated eventsare processed throughasimulationoftheCMSdetectorbasedon Geant4 [52].

The reconstruction of events relies on the particle-flow (PF) algorithm [53], which combines information from the CMS sub-detectors toidentify andreconstructtheparticles emerging from pp collisions: chargedand neutralhadrons, photons, muons, and electrons.CombinationsofthesePFobjectsareusedtoreconstruct higher-levelobjectssuchasjets,

τ

hcandidates,andmissing

trans-versemomentum.

ElectronsarereconstructedbymatchingECALclusterstotracks inthetracker.Theyarethen identifiedwithamultivariate analy-sis (MVA)discriminantthatmakes useofvariablesrelatedto the

energydepositsintheECAL,thequalityofthetrack,andthe com-patibilitybetweenthepropertiesoftheECALclustersandthetrack that havebeen matched [54]. The MVAworkingpoint chosen in thissearch has an efficiency ofabout 80%.The reconstruction of muon candidates is performedcombiningthe information ofthe trackerandthemuon systems.Muons arethen identified onthe basis of the track reconstruction quality and on the number of measurementsinthetrackerandthemuonsystems [55].The rel-ativeisolationofelectronsandmuonsisdefinedas:

I

≡



chargedpT

+

max



0

,



_neutralpT

−

1₂



charged,PUpT



p T

.

(1)

In this formula,



_chargedpT is the scalar sum of the transverse

momentaofthe chargedparticles,excluding thelepton itself, as-sociatedwiththeprimaryvertexandinaconearoundthelepton direction,withsize



R

=

√

(

η

)

2

_{+ (φ)}

2

₌

₀

_.

_{3 forelectrons, or}

0.4formuons. The sum



_neutralpT representsa similar quantity

forneutralparticles.ThelasttermcorrespondstothepTofneutral

particlesfrompileupvertices,which,asestimatedfromsimulation, is equal to approximately half of that of charged hadrons asso-ciated withpileup vertices,denoted by



_charged,PUpT. The pT of

thelepton isdenoted p

T.Theazimuthal angle,

φ

,ismeasured in

radians.

JetsarereconstructedfromPFobjectswiththeanti-kT

cluster-ing algorithmimplementedin the FastJet library[56,57],usinga distanceparameterof0.4.Correctionstothejetenergyareapplied asafunctionofthepTand

η

ofthejet [58].Thejetsinthissearch

are requiredto be separatedfrom theselected electrons, muons, or

τ

h, by



R

≥

0

.

5. Jets that originate from b quarks, called b

jets, are identified with the combined secondary vertex (CSVv2) algorithm [59]. The CSVv2 algorithm builds a discriminant from variables related to secondary vertices associated with the jet if any,andfromtrack-basedlifetimeinformation.Theworkingpoint choseninthissearchprovidesanefficiencyforb quarkjetsof ap-proximately70%,andamisidentificationrateforlight-flavorandc quarkjetsofapproximately1and10%,respectively.

Hadronically decaying

τ

leptons are reconstructed with the hadrons-plus-strips (HPS) algorithm [60,61] as a combination of tracks and energy deposits in strips of the ECAL.The tracks are the signature of the charged hadrons, andthe strips that of the neutral pions, which decay to a pair of photons with potential electron–positron conversion. The reconstructed

τ

h decay modes

are one track, one trackplusat leastone strip, andthreetracks. Therateforjetstobe misidentifiedas

τ

h isreducedby applying

an MVAdiscriminatorthat usesisolation aswell aslifetime vari-ables.Its workingpoint hasbeenchosen tohave anefficiencyof approximately45% fora misidentificationrate oflight-flavor jets of the orderof 0.1%. Additionally, discriminatorsthat reduce the rateswithwhichelectronsandmuonsare misidentifiedas

τ

hare

applied. Loose working points with an efficiency above 90% are chosen because the Z

→

ee

/

μμ

background does not contribute muchintheregionwherethesignalisexpected.

Toaccountforthecontributionofundetectedparticles,suchas theneutrinos,themissingtransversemomentum,



pmiss_T ,isdefined asthenegativevectorialsumofthetransversemomentaofallPF objects reconstructed in the event. The magnitude ofthis vector isdenoted pmiss_T . The reconstructedvertex withthe largestvalue ofsummedphysics-object p2_T istakentobetheprimary pp inter-action vertex. The physics objects are the objects constructed by ajet findingalgorithm [56,62] applied toall chargedtracks asso-ciated withthevertex, and thecorresponding associated missing transversemomentum.

Table 1

Baseline selectioncriteriaforobjectsrequiredinvarious fi-nalstates.Thenumbersgivenforthe pT thresholdsofthe electronand muonintheeμfinalstatecorrespondtothe leadingandsubleadingparticles.ThepTthresholdfortheτh candidates istheresultofanoptimization oftheexpected exclusionlimitsofthesignal.

eμ eτh μτh

pT(e) >24/13 GeV >26 GeV —

pT(μ) >24/13 GeV — >20 GeV

pT(τh) — >25 GeV >25 GeV

pT(b) >20 GeV >20 GeV >20 GeV

|η(e)| <2.4 <2.1 — |η(μ)| <2.4 — <2.1 |η(τh)| — <2.3 <2.3 |η(b)| <2.4 <2.4 <2.4 Isolation (e) <0.10 <0.10 — Isolation (μ) <0.15 — <0.15 Ident. (τh) — MVA MVA

4. Eventselection

Events are selectedinthree different

τ τ

final states:eμ,eτh,

and

μτ

h. They are additionally required to contain at least one

b-taggedjet.Thedominantbackgroundswiththeseobjectsinthe finalstatearett andZ

→

τ τ

production.Anotherlargebackground consistsof eventswithjetsmisidentified as

τ

h,such asW

+

jets

events,thebackgroundfromSMeventscomposeduniquelyofjets producedthroughthestronginteraction,referredtoasQCD multi-jetevents,orsemileptonictt events.

All eventsare requiredto haveat leastone b-taggedjet with pT

>

20GeV and

|

η

|

<

2

.

4.About 90% of simulatedsignal events

passing thiscondition haveonly one such jet, asa resultof the typically soft b jet pT spectrum and of the limited efficiency of

the b taggingalgorithm. Eventsinthe eμ final stateare selected withatriggerthatreliesonthepresenceofbothanelectronand a muon, wherethe leading leptonhas pT

>

23GeV andthe

sub-leading one pT

>

12GeV if it is an electron or 8GeV if it is a

muon. Intheeτh finalstate, thetriggerisbasedon thepresence

of an isolatedelectron with pT

>

25GeV,whereas in the

μτ

h

fi-nal state events are selected witha combination oftriggers that requireeitheranisolatedmuonwithpT

>

22GeV,oramuonwith pT

>

19GeV anda

τ

hcandidatewithpT

>

21GeV.Duringthe2016

datatakingperiod,noneoftheavailabletriggersthatrequiredthe presenceofbothanelectronanda

τ

hcandidatecouldincreasethe

signalacceptancesignificantlywithrespecttothetriggerbasedon thepresenceofan electrononly.Tighter selectioncriteriaare ap-pliedatthereconstructionlevel.Theelectrons,muons,and

τ

h

can-didatesarerequiredtobewellidentifiedandisolated [54,55,61],to haveoppositecharge, andtobeseparatedbyatleast



R

=

0

.

4 if thereisa

τ

h,or0.3otherwise.Table1detailsthe pT,

η

,isolation,

andidentification criteriaforthe various objects,inthe different finalstates.

Toincrease the sensitivityoftheanalysis, eventsin eachfinal state are separated into four categories with different signal-to-background ratios.The categoriesare definedonthe basis ofthe invariant massofthevisibledecayproductsofthe

τ

leptonsand the b-taggedjet withthe highestpT,denotedbymvisbτ τ .This vari-able is typically low for signal events because the three objects originate froma 125GeV Higgs boson,butit isonaverage much largerforbackgroundevents,wherethethreeobjectsdonot orig-inatefromadecayofaresonance,asshowninFig.2forthe

μτ

h

finalstate.Thethresholdsthatdefinethecategoriesdependonthe

τ τ

final state:they are lowerinthe eμfinal state becausethere aremoreneutrinosnotincludedinthemasscalculation,andthey are higher in the eτh final state to keep enough events despite

Fig. 2. Visibleinvariantmassoftheleptonsandtheleadingb jet,mvis

bτ τ,afterthe baselineselection,inthe μτh finalstate, forthe signalwithdifferentmass hy-potheses(top).Distributionofmvis

bτ τintheμτhfinalstate(bottom).The“jet→τh” contributionincludesalleventswithajetmisidentifiedasaτhcandidate,whereas therestofbackgroundcontributionsonlyincludeeventswherethereconstructed τhcorrespondstoaτh,amuon,oranelectron,atthegeneratorlevel.The“Other” contributionincludeseventsfromsingletopquark,diboson,andSMHiggsboson processes.Thesignalhistogramcorrespondsto10timestheSMproductioncross sectionforggh,VBF,andVh processes,andassumesB(h→aa→2τ2b)=100%. (Forinterpretationofthe colorsinthefigures,thereaderisreferredtotheweb versionofthisarticle.)

Signaleventswithma



25GeV contributemostlytothefirsttwo

categories, whereas those with ma



25GeV are concentrated in

thesecond andthirdcategories.Thiscanbeexplainedbythefact thatthemissing b jetin themasscalculation wouldbe closerto thereconstructedb jet fora signalwithlowermabecauseofthe

boostofthepseudoscalarbosons,leadingtoalargerreconstructed mass.Thelastcategoryhaslargebackgroundyields;itisusefulto constrain the various backgrounds and provides some additional sensitivityforlow-masignalsamples.Theresultsofthesearchare

extractedfroma fitofthevisible

τ τ

mass(mvis

τ τ )distributionsin eachof thecategories, because thisisa resonant distributionfor signalevents.

Selectioncriteriaareappliedtooptimizetheexpectedlimitson theproductofthesignalcrosssectionandbranchingfraction.The samethresholdswouldbeobtainedwithanoptimizationbasedon thediscovery potential.One suchcriterion isbased onthe trans-versemassof



pmiss_T andeach oftheleptons.The transversemass mTbetweenalepton



and



pmissT isdefinedas

mT

(,



pmissT

)

≡



2p_Tpmiss_T

[

1

−

cos

(φ)

],

(2)

where p_Tisthetransversemomentumofthelepton



,and

φ

is theazimuthalanglebetweentheleptonmomentumand



pmiss_T . Se-lectingeventswithlowmTstronglyreducesthebackgroundsfrom

W

+

jets andtt events,which arecharacterizedby alarger p



miss_T . Inaddition,forW

+

jets eventsinwhichtheselectedleptoncomes fromtheW bosondecay,mThasaJacobianpeakneartheW boson

mass. The distributions of mT

(

μ

,



pmissT

)

and mT

(

τ

h

,



pmissT

)

in the

μτ

hfinalstatebeforethemvisbτ τ -basedcategorizationareshownin Fig.3(topandcenter).

Anotherselectioncriterion isbasedonthe variable Dζ,which

isdefinedas

Dζ

≡

pζ

−

0

.

85 pvisζ

,

(3)

where pζ is the component of



pmissT along the bisector of the

transversemomenta ofthe two

τ

candidatesand pvis_ζ isthesum ofthecomponentsofthelepton pT alongthesamedirection [63].

AsshowninFig.3(bottom),theZ

→

τ τ

backgroundtypicallyhas Dζ valuesclose to zero because



pmissT is approximately collinear

to the

τ τ

system, whereas the tt background is concentrated at lower Dζ valuesbecause oftypically large



pmissT notalignedwith

the

τ τ

system. The signal liesinan intermediate region because



pmiss

T is approximatelyaligned with the

τ τ

system, but pmissT is

usuallysmall.Theprecisecriteriaforeachfinalstateandcategory areindicatedinTable2.

5. Backgroundestimation

TheZ

→ 

backgroundisestimatedfromsimulation.The dis-tributionsofthepTofthedileptonsystemandthevisibleinvariant

mass between the leptons and the leading b jet are reweighted with corrections derived using data from a region enriched in Z

→

μμ

+ ≥

1 b events. The simulation is separated between Z

→

τ τ

, where the reconstructed

τ

candidates correspond to

τ

leptons atgeneratorlevel,andZ

→

ee

/

μμ

decays,whereatleast oneelectronormuonismisidentifiedasa

τ

hcandidate.

Backgroundswithajetmisidentifiedasa

τ

hcandidateare

esti-matedfromdata.TheyconsistmostlyofW

+

jets andQCDmultijet events,aswellasthefractionoftt,diboson,andsingletopquark productionwherethereconstructed

τ

hcandidatecomesfromajet.

Theprobabilitiesforjetsto bemisidentifiedas

τ

hcandidates,

de-noted f , areestimated fromZ

→

μμ

+

jets eventsin data.They are parameterized withLandaudistributions asa function ofthe pT ofthe

τ

h candidate,separatelyfor everyreconstructed

τ

h

de-cay mode. Events that pass all the selection criteria, except that the

τ

h candidatefailstheisolation condition,arereweightedwith

aweight f

/(

1

−

f

)

toestimatethecontributionofeventswithjets inthesignalregion.Thecontributionofeventswithgenuine elec-trons, muons, or

τ

h candidates inthecontrol region isestimated

fromsimulationandsubtractedfromdata.

Intheeμfinalstate,thesmallW

+

jets backgroundisestimated fromsimulation [64].Sucheventstypicallyhaveagenuinelepton coming from the W boson decay and a jet misidentified asthe other lepton. The QCD multijet background, which also contains jets misidentified asleptons, isestimated from data.Its normal-ization corresponds to the difference between the data and the sumofall theother backgroundsina so-calledsame-signregion where the

τ

candidates have the same sign. A smooth distribu-tionisobtainedbyadditionallyrelaxingtheisolationconditionsof bothleptons.Acorrectionthatisextractedfromdataisappliedto extrapolatethenormalizationobtainedinthesame-sign regionto thesignalregion.

Fig. 3. DistributionsofmT(μ,pmissT )(top),mT(τh,



pmissT )(center),andDζ (bottom) intheμτhfinalstatebeforethem_{bτ τ}vis-basedcategorization.The“jet→τh” contri-butionincludesalleventswithajetmisidentifiedasaτhcandidate,whereasthe restofbackgroundcontributionsonlyincludeeventswherethereconstructedτh correspondstoaτh, amuon,oranelectron,atthegenerator level.The“Other” contributionincludeseventsfromsingletopquark,diboson,andSMHiggsboson processes.Thesignalhistogramcorrespondsto10timestheSMproductioncross sectionforggh,VBF,andVh processes,andassumesB(h→aa→2τ2b)=100%.

Table 2

Optimizedselectionandcategorizationinthevariousfinalstates.Theselection cri-terion Dζ >−30GeV in the eμ finalstatereduces the largett background.In the otherfinalstatesthe tt backgroundisless important,and onlyeventswith

Dζ>0GeV arediscardedinoneofthecategoriesoftheμτhfinalstatetoreduce theZ→τ τbackground.Thisselectioncriteriondoesnotimprovethesensitivityin theeτhfinalstatebecauseofthelowerexpectedsignalandbackgroundyields,and isthereforenotapplied.

Variable Category 1 Category 2 Category 3 Category 4 eμ

mvis_{bτ τ} <65 GeV ∈[65,80]GeV ∈[80,95]GeV >95 GeV

mT(e,pmissT ) <40 GeV <40 GeV <40 GeV <40 GeV

mT(μ,pmissT ) <40 GeV <40 GeV <40 GeV <40 GeV

Dζ >−30 GeV >−30 GeV >−30 GeV >−30 GeV eτh

mvis

bτ τ <80 GeV ∈[80,100]GeV ∈[100,120]GeV >120 GeV

mT(e,pmissT ) <40 GeV <50 GeV <50 GeV <40 GeV

mT(τh,pTmiss) <60 GeV <60 GeV <60 GeV <60 GeV μτh

mvis

bτ τ <75 GeV ∈[75,95]GeV ∈[95,115]GeV >115 GeV

mT(μ,pmissT ) <40 GeV <50 GeV <50 GeV <40 GeV

mT(τh,pTmiss) <60 GeV <60 GeV <60 GeV <60 GeV

Dζ — <0 GeV — —

Otherprocesses,includingdiboson,tt,andsingletopquark pro-duction without jet misidentified as a

τ

h candidate, as well as

SMHiggsbosonprocessesinvariousproductionanddecaymodes, areestimatedfromsimulation.Thett productionisamajor back-ground, especiallyinthe eμfinal state. Thett simulation models thevariablesusedinthisanalysiswell,asithasbeenverifiedina controlregionintheeμfinalstatewherenoselectioncriterionis applied onmT

(

e

,



pmissT

)

ormT

(

μ

,



pmissT

)

,andwhere the Dζ

selec-tioncriterionisinverted.

Inthe eτhand

μτ

h final states,whereallbackgrounds witha

jet misidentified asa

τ

h candidateare estimatedfromdata,

sim-ulated eventswith a reconstructed

τ

h that is not matched toan

electron, a muon,or a

τ

h atthe generatorlevel are discarded to

avoid doublecounting. Approximately 30% ofsimulatedtt events aftertheselectionhaveareconstructed

τ

h thatisnotmatchedto

anelectron,amuon,ora

τ

hatthegeneratorlevel.

6. Fitmethodandsystematicuncertainties

The search for an excess of signal events over the expected backgroundinvolvesaglobalbinnedmaximumlikelihoodfitbased on themvis_{τ τ distributions}inthedifferentchannelsandcategories. Thestatisticaluncertaintylargelydominatesoversystematic uncer-taintiesinthissearch.Thesystematicuncertaintiesarerepresented by nuisance parameters that are varied in the fit according to their probability densityfunctions. Alog-normal probability den-sity function is assumedfor the nuisance parameters that affect the event yields of the various background andsignal contribu-tions,whereassystematicuncertaintiesthataffectthedistributions arerepresentedbynuisanceparameterswhosevariationresultsin acontinuousperturbationofthespectrum [65] andwhichare as-sumedtohaveaGaussianprobabilitydensityfunction.

Totakeintoaccountthelimitedsizeofsimulatedsamplesand ofdatainthecontrolregions usedtoestimate someofthe back-groundprocesses,statisticaluncertainties inindividualbinsofthe mvis_{τ τ distributions} are considered asPoissonian nuisance parame-ters.The uncertaintycanbe aslarge as40%forsome binsinthe low-mvis_{bτ τ categories.}Thecombinedeffectofalltheseuncertainties isthedominantsystematicuncertaintyinthissearch.

The uncertainties inthe jet energy scale [58] affect the over-all yieldsofprocessesestimatedfromsimulation,aswell astheir

Fig. 4. Distributionsofmvis

τ τinthefourcategoriesoftheeμchannel.The“Other”contributionincludeseventsfromsingletopquark,diboson,SMHiggsboson,andW+jets productions.ThesignalhistogramcorrespondstotheSMproductioncrosssectionforggh,VBF,andVh processes,andassumesB(h→aa→2τ2b)=10%.Thenormalizations ofthepredictedbackgrounddistributionscorrespondtotheresultoftheglobalfit.

relativecontribution tothe differentcategories becausethe cate-gorizationisbasedon thevalueofmvis_{bτ τ for}each event.Theyare functionsof the jet pT and

η

.The



pmissT is recomputedfor each

variationofthe jet energyscale.The uncertaintyin



pmiss T related

tothemeasurementoftheenergythatisnotclusteredinjets [66] isevaluatedevent-by-event,andisalsoconsideredasashape un-certainty.

Correctionsfortheefficiencyofthe identificationofelectrons, muons, and

τ

h candidates are derived from data using

tag-and-probe methods [67], and are applied to simulated events as a functionofthelepton pTand

η

.Uncertaintiesrelatedtothese

cor-rectionsamountto2% forelectrons, 2%formuons,and5% for

τ

h

candidates.Additionally,eventswithanelectronormuon misiden-tifiedasa

τ

hcandidatehaveayielduncertaintyof5%.Triggerscale

factorsare also estimatedwithtag-and-probe methods and their corresponding uncertainties in the yields of simulated processes are1%.

Theenergyscale of

τ

h candidatesiscorrected foreach

recon-structeddecay mode,andthe uncertaintyof 1.2%for each single decay mode is considered as a shape uncertainty. Uncertainties intheenergyscales ofelectrons andmuonsare alsoincludedas shapeuncertainties.

Correctionstotheefficiencyforidentifyingab quarkjetasab jet,aswellasformistaggingajetoriginatingfromadifferent

fla-vor,areappliedtosimulatedeventsonthebasisofthegenerated flavorofthejets.Theuncertaintiesinthescalefactorsdependon the pT ofthejetandarethereforeconsideredasshape

uncertain-ties. Theyamountto1.5%forajetoriginatingfroma b quark,5% fromac quark,and10%fromalight-flavorparton [59].

The uncertainty in the yield of the backgrounds with jets misidentified as

τ

h candidates accounts for possibly different

misidentification rates in Z

+

jets events (where the misidenti-fication rates are measured), and in W

+

jets and QCD multijet events (which dominate the constitution of the reducible back-groundinthesignalregion),andfordifferencesbetweendataand predictedbackgroundsobservedinaregion enrichedinreducible backgroundevents byinverting thecharge requirementon the

τ

candidates and removing the mT and Dζ selection criteria. This

uncertaintyamounts to20%,andisconstrainedtoabout7% after themaximumlikelihoodfitbecauseofthelargenumberofevents contributingtothelastmvis_{bτ τ category.}Uncertaintiesinthe param-eterizationofthemisidentificationprobabilityofjetsasafunction of pT resultin shapeuncertainties for thebackgrounds withjets

misidentifiedas

τ

hcandidates.

TheuncertaintyintheyieldoftheQCDmultijetbackgroundin theeμfinalstateis20%;thevaluecomesfromtheuncertaintyin theextrapolationfactorfromthesame-signregiontothe opposite-sign region. The uncertainty in the W

+

jets background in this channelalsoamountsto20%,andaccountsforapotential

mismod-Fig. 5. Distributionsofmvis

τ τ inthefourcategoriesoftheeτhchannel.The“jet→τh”contributionincludesalleventswithajetmisidentifiedasaτhcandidate,whereasthe restofbackgroundcontributionsonlyincludeeventswherethereconstructedτhcorrespondstoaτh,amuon,oranelectron,atthegeneratorlevel.The“Other”contribution includeseventsfromsingletopquark,diboson,andSMHiggsbosonprocesses.ThesignalhistogramcorrespondstotheSMproductioncrosssectionforggh,VBF,andVh processes,andassumesB(h→aa→2τ2b)=10%.Thenormalizationsofthepredictedbackgrounddistributionscorrespondtotheresultoftheglobalfit.

elinginsimulationofthemisidentificationrateofjetsaselectrons ormuons.

The theoretical yield uncertainty of the tt background is re-latedtothePDF uncertaintyandtothe uncertaintyassociatedto the strong couplingconstant

α

S in thefull NNLO plus NNLL

or-der calculation ofthecross section;it amountsto about4%. The yield uncertainties for other backgrounds estimated from simu-lationare taken fromrecentCMS measurements:6% for diboson processes [68],13%forsingletopquarkprocesses [69],and7%for Z

+

jets eventswithatleastoneb-taggedjetinthefinalstate [70]. TheuncertaintyinthecorrectionofthedileptonpTdistributionfor

Drell–Yaneventsisequalto10%ofthesizeofthecorrectionitself. Theuncertaintyinthecorrectionofthemvis_{bτ τ distribution}isequal tothecorrectionitself,andconsideredasashapeuncertainty. Un-certaintiesintheproductioncrosssectionsandbranchingfractions forSMHiggsbosonprocessesaretakenfromRef. [71].The uncer-taintyintheintegratedluminosityamountsto2.5% [72].

7. Results

Themvis_{τ τ distributions}inthe differentchannelsandcategories areshowninFigs.4–6.Thebinningcorresponds tothebinsused inthelikelihoodfit.

No excess is observed relatively to the SM background pre-diction. Upper limits at 95% CL are set on

(

σ

(

h

)/

σ

SM

)B(

h

→

aa

→

2τ2b

)

using the modified frequentist construction CLs in

the asymptotic approximation [73–77], for pseudoscalar masses between 15 and60GeV.In this expression,

σ

SM denotes theSM

productioncross sectionoftheHiggsboson, whereas

σ

(

h

)

isthe h productioncrosssection.Thelimitsperchannelandforthe com-binationofthethreechannelsare showninFig.7.The most sen-sitivefinalstateis

μτ

h.Thesensitivityoftheeτhandeμchannels

is approximatelyequivalent; thefirst channel suffersfromhigher trigger thresholds and lower object identification efficiency than

μτ

h,andthe second onesuffers fromalower branching fraction

than

μτ

h. At low ma, the eμ final state hasa highersignal

ac-ceptancethanthe otherfinal states,especially eτh.Thelimitsare

more stringent in the intermediate mass range. The low-ma

sig-nalshavealoweracceptancebecauseoftheoverlapoftheleptons related to the boost ofthe pseudoscalar bosons, andof the typ-ically softer lepton andb jet pT spectra. The highma signalslie

in a region where more backgrounds contribute, leading also to lower sensitivitythan inthe intermediate massregion. The cate-gories are complementary over the probed mass range,with the low-mvis_{bτ τ signal}regionsmoresensitiveforheavyresonances,and thehigh-mvis

Fig. 6. Distributionsofmvis

τ τinthefourcategoriesoftheμτhchannel.The“jet→τh”contributionincludesalleventswithajetmisidentifiedasaτhcandidate,whereasthe restofbackgroundcontributionsonlyincludeeventswherethereconstructedτhcorrespondstoaτh,amuon,oranelectron,atthegeneratorlevel.The“Other”contribution includeseventsfromsingletopquark,diboson,andSMHiggsbosonprocesses.ThesignalhistogramcorrespondstotheSMproductioncrosssectionforggh,VBF,andVh processes,andassumesB(h

→

aa→2τ2b)

=

10%.Thenormalizationsofthepredictedbackgrounddistributionscorrespondtotheresultoftheglobalfit.

The combined limit at intermediate mass is aslow as3% on

B(

h

→

aa

→

2τ2b

)

,assumingtheSMproductioncrosssectionand mechanisms forthe Higgs boson, and isup to 12% for the low-est mass point ma

=

15GeV. Computing the branching fractions

of the light pseudoscalar to SM particles [15,78], this translates to limits on

(

σ

(

h

)/

σ

SM

)

B(

h

→

aa

)

of about 20% in 2HDM

+

S

type II—including the NMSSM—with tan

β >

1 for ma

=

40GeV.

Thisimprovesbymorethanoneorderofmagnitudeprevious lim-itson

B(

h

→

aa

)

obtainedinthe2μ2τ finalstatebyCMSfor15

<

ma

<

25GeV [20,23], andby upto afactorfivethoseobtainedin

the2μ2b finalstatebyCMSfor25

<

ma

<

60GeV [20].Inthe

sce-nariowiththehighestbranchingfraction,2HDM

+

Stype III with tan

β

=

2,theexpected limitis aslow as6%at intermediatema.

Fig.8showstheobservedlimitsat95% CL on

(

σ

(

h

)/

σ

SM

)B(

h

→

aa

)

asafunctionofmaandtan

β

fortype IIIandtype IV2HDM

+

S,

forwhichthereisastrongdependencewithtan

β

.Fig.9showsthe observedlimitsat95%CL on

(

σ

(

h

)/

σ

SM

)B(

h

→

aa

)

forafew

sce-nariosof2HDM

+

S,assumingthebranchingfractionsofthelight pseudoscalar to SM particles computed using Refs. [15,78]. The limit shownfortype II2HDM

+

S is approximatelyvalidfor any valueoftan

β >

1,andthatfortype I2HDM

+

Sdoesnotdepend ontan

β

. Inthema rangeconsideredin theanalysis, the

branch-ingfraction

B(

aa

→

bbτ τ

)

rangesbetween0.10and0.11intype I 2HDM

+

S,between0.11and0.13fortan

β

=

2 intype II2HDM

+

S,

between0.44and0.46fortan

β

=

2 intype III2HDM

+

S,and be-tween0.16and0.21fortan

β

=

0

.

5 intype IV2HDM

+

S.

8. Summary

ThefirstsearchforexoticdecaysoftheHiggsbosontopairsof light bosons with two b quark jets andtwo

τ

leptons inthe fi-nal state hasbeen performedwith 35

.

9fb−1 ofdata collected at 13TeV center-of-mass energy in 2016. This decay channel has a large branching fraction in manymodels where the couplings to fermions are proportional to the fermion mass,and can be trig-gered withhighefficiency inthe dominantgluon fusion produc-tion modebecauseof thepresenceof lightleptons fromleptonic

τ

decays. No excess of events is found on top of the expected standardmodelbackgroundformassesofthelightboson,ma,

be-tween 15 and 60GeV. Upper limits between 3 and 12% are set on the branching fraction

B(

h

→

aa

→

2τ2b

)

assuming the SM productionofthe Higgsboson.This translatestoupperlimitson

B(

h

→

aa

)

as low as20% forma

=

40GeV in the NMSSM.These

resultsimprove by morethan one orderofmagnitudethe sensi-tivitytoexoticHiggsbosondecaysto pairsoflightpseudoscalars intheNMSSMfrompreviousCMSresultsinother finalstatesfor 15

<

ma

<

25GeV,andbyafactoruptofivefor25

<

ma

<

60GeV

Fig. 7. Expectedandobserved95%CL limitson(σ(h)/σSM)B(h→aa→2τ2b)in%.Theeμresultsareshowninthetopleftpanel,eτhinthetopright,μτhinthebottom left,andthecombinationinthebottomright.Theinner(green)bandandtheouter(yellow)bandindicatetheregionscontaining68and95%,respectively,ofthedistribution oflimitsexpectedunderthebackground-onlyhypothesis.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technicalandadministrativestaffs atCERN andatother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectivelythe computinginfrastructureessential to ouranalyses. Finally, we acknowledge the enduring support for the construc-tionandoperation oftheLHCandthe CMSdetectorprovidedby thefollowingfundingagencies:BMWFWandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIEN-CIAS(Colombia);MSESandCSF(Croatia);RPF(Cyprus);SENESCYT (Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Fin-land,MEC,andHIP(Finland);CEAandCNRS/IN2P3(France);BMBF, DFG, andHGF (Germany); GSRT (Greece);NKFIA (Hungary); DAE andDST (India);IPM (Iran);SFI (Ireland);INFN (Italy); MSIP and NRF(RepublicofKorea);LAS(Lithuania);MOEandUM(Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, ROSATOM, RAS and RFBR (Russia); MESTD (Serbia); SEIDI, CPAN, PCTI and FEDER (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA (Thailand); TÜBITAK and TAEK (Turkey);

NASU andSFFR (Ukraine); STFC (United Kingdom);DOEand NSF (USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandHorizon2020Grant, contract No. 675440 (European Union); the Leventis Founda-tion; the Alfred P. Sloan Foundation; the Alexander von Hum-boldt Foundation; the Belgian Federal Science Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excellence of Science – EOS” – be.h projectNo. 30820817;theMinistryofEducation,YouthandSports (MEYS) of the Czech Republic; the Lendület (“Momentum”) Pro-gramme and the János Bolyai Research Scholarship of the Hun-garian Academy of Sciences, the New National Excellence Pro-gram ÚNKP, the NKFIA research grants 123842, 123959, 124845, 124850 and 125105 (Hungary); the Council of Science and In-dustrial Research,India;theHOMING PLUSprogramofthe Foun-dation for Polish Science, cofinanced from European Union, Re-gional Development Fund, the Mobility Plus program of the Ministry of Science and Higher Education, the National Science Centre (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus 2014/13/B/ST2/02543, 2014/15/B/ST2/03998, and 2015/19/B/ST2/ 02861,Sonata-bis2012/07/E/ST2/01406;theNationalPriorities Re-search Program by Qatar National Research Fund; the Programa Estatal de Fomento de la Investigación Científica y Técnica de

Fig. 8. Observed95%CL limitson(σ(h)/σSM)B(h→aa)in2HDM+Softype III (top),andtype IV(bottom).Thecontourscorrespondingtoa95%CL exclusionof

(σ(h)/σSM)B(h

→

aa)

=

1.00 and 0.34aredrawnwith dashed lines.The num-ber34%correspondstothelimitonthebranchingfractionoftheHiggsbosonto beyond-the-SMparticlesatthe95%CL obtainedwithdatacollectedat center-of-massenergiesof7and8TeV bytheATLASandCMSexperiments [10].

Fig. 9. Observed95%CL limitson(σ(h)/σSM)B(h

→

aa)forvarious2HDM+Stypes. Thelimitintype I2HDM+Sdoesnotdependontanβ.

ExcelenciaMaríade Maeztu,grant MDM-2015-0509andthe Pro-grama Severo Ochoa del Principado de Asturias; the Thalis and Aristeiaprograms cofinancedby EU-ESF andthe GreekNSRF; the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chula-longkornUniversityandtheChulalongkornAcademic intoIts2nd CenturyProjectAdvancement Project(Thailand);theWelch Foun-dation,contractC-1845;andtheWestonHavensFoundation(USA).

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TheCMSCollaboration

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

F. Ambrogi,

E. Asilar,

T. Bergauer,

J. Brandstetter,

E. Brondolin,

M. Dragicevic,

J. Erö,

A. Escalante Del Valle,

M. Flechl,

R. Frühwirth

1

,

V.M. Ghete,

J. Hrubec,

M. Jeitler

1

,

N. Krammer,

I. Krätschmer,

D. Liko,

T. Madlener,

I. Mikulec,

N. Rad,

H. Rohringer,

J. Schieck

1

,

R. Schöfbeck,

M. Spanring,

D. Spitzbart,

A. Taurok,

W. Waltenberger,

J. Wittmann,

C.-E. Wulz

1

,

M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Chekhovsky,

V. Mossolov,

J. Suarez Gonzalez

InstituteforNuclearProblems,Minsk,Belarus

E.A. De Wolf,

D. Di Croce,

X. Janssen,

J. Lauwers,

M. Pieters,

M. Van De Klundert,

H. Van Haevermaet,

P. Van Mechelen,

N. Van Remortel

UniversiteitAntwerpen,Antwerpen,Belgium

S. Abu Zeid,

F. Blekman,

J. D’Hondt,

I. De Bruyn,

J. De Clercq,

K. Deroover,

G. Flouris,

D. Lontkovskyi,

S. Lowette,

I. Marchesini,

S. Moortgat,

L. Moreels,

Q. Python,

K. Skovpen,

S. Tavernier,

W. Van Doninck,

P. Van Mulders,

I. Van Parijs

VrijeUniversiteitBrussel,Brussel,Belgium

D. Beghin,

B. Bilin,

H. Brun,

B. Clerbaux,

G. De Lentdecker,

H. Delannoy,

B. Dorney,

G. Fasanella,

L. Favart,

R. Goldouzian,

A. Grebenyuk,

A.K. Kalsi,

T. Lenzi,

J. Luetic,

N. Postiau,

E. Starling,

L. Thomas,

C. Vander Velde,

P. Vanlaer,

D. Vannerom,

Q. Wang

UniversitéLibredeBruxelles,Bruxelles,Belgium

T. Cornelis,

D. Dobur,

A. Fagot,

M. Gul,

I. Khvastunov

2

,

D. Poyraz,

C. Roskas,

D. Trocino,

M. Tytgat,

W. Verbeke,

B. Vermassen,

M. Vit,

N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,

O. Bondu,

S. Brochet,

G. Bruno,

C. Caputo,

P. David,

C. Delaere,

M. Delcourt,

B. Francois,

A. Giammanco,

G. Krintiras,

V. Lemaitre,

A. Magitteri,

A. Mertens,

M. Musich,

K. Piotrzkowski,

A. Saggio,

M. Vidal Marono,

S. Wertz,

J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

F.L. Alves,

G.A. Alves,

L. Brito,

G. Correia Silva,

C. Hensel,

A. Moraes,

M.E. Pol,

P. Rebello Teles

E. Belchior Batista Das Chagas,

W. Carvalho,

J. Chinellato

3

,

E. Coelho,

E.M. Da Costa,

G.G. Da Silveira

4

,

D. De Jesus Damiao,

C. De Oliveira Martins,

S. Fonseca De Souza,

H. Malbouisson,

D. Matos Figueiredo,

M. Melo De Almeida,

C. Mora Herrera,

L. Mundim,

H. Nogima,

W.L. Prado Da Silva,

L.J. Sanchez Rosas,

A. Santoro,

A. Sznajder,

M. Thiel,

E.J. Tonelli Manganote

3

,

F. Torres Da Silva De Araujo,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahuja

a

,

C.A. Bernardes

a

,

L. Calligaris

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

S.F. Novaes

a

,

Sandra S. Padula

a

,

D. Romero Abad

b

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b

UniversidadeFederaldoABC,SãoPaulo,Brazil

A. Aleksandrov,

R. Hadjiiska,

P. Iaydjiev,

A. Marinov,

M. Misheva,

M. Rodozov,

M. Shopova,

G. Sultanov

InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

A. Dimitrov,

L. Litov,

B. Pavlov,

P. Petkov

UniversityofSofia,Sofia,Bulgaria

W. Fang

5

,

X. Gao

5

,

L. Yuan

BeihangUniversity,Beijing,China

M. Ahmad,

J.G. Bian,

G.M. Chen,

H.S. Chen,

M. Chen,

Y. Chen,

C.H. Jiang,

D. Leggat,

H. Liao,

Z. Liu,

F. Romeo,

S.M. Shaheen,

A. Spiezia,

J. Tao,

C. Wang,

Z. Wang,

E. Yazgan,

H. Zhang,

J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

Y. Ban,

G. Chen,

A. Levin,

J. Li,

L. Li,

Q. Li,

Y. Mao,

S.J. Qian,

D. Wang,

Z. Xu

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

Y. Wang

TsinghuaUniversity,Beijing,China

C. Avila,

A. Cabrera,

C.A. Carrillo Montoya,

L.F. Chaparro Sierra,

C. Florez,

C.F. González Hernández,

M.A. Segura Delgado

UniversidaddeLosAndes,Bogota,Colombia

B. Courbon,

N. Godinovic,

D. Lelas,

I. Puljak,

T. Sculac

UniversityofSplit,FacultyofElectricalEngineering,MechanicalEngineeringandNavalArchitecture,Split,Croatia

Z. Antunovic,

M. Kovac

UniversityofSplit,FacultyofScience,Split,Croatia

V. Brigljevic,

D. Ferencek,

K. Kadija,

B. Mesic,

A. Starodumov

6

,

T. Susa

InstituteRudjerBoskovic,Zagreb,Croatia

M.W. Ather,

A. Attikis,

M. Kolosova,

G. Mavromanolakis,

J. Mousa,

C. Nicolaou,

F. Ptochos,

P.A. Razis,

H. Rykaczewski,

D. Tsiakkouri

UniversityofCyprus,Nicosia,Cyprus

M. Finger

7

,

M. Finger Jr.

7

E. Ayala

EscuelaPolitecnicaNacional,Quito,Ecuador

E. Carrera Jarrin

UniversidadSanFranciscodeQuito,Quito,Ecuador

H. Abdalla

8

,

A.A. Abdelalim

9

,

10

,

A. Mohamed

10

AcademyofScientificResearchandTechnologyoftheArabRepublicofEgypt,EgyptianNetworkofHighEnergyPhysics,Cairo,Egypt

S. Bhowmik,

A. Carvalho Antunes De Oliveira,

R.K. Dewanjee,

K. Ehataht,

M. Kadastik,

M. Raidal,

C. Veelken

NationalInstituteofChemicalPhysicsandBiophysics,Tallinn,Estonia

P. Eerola,

H. Kirschenmann,

J. Pekkanen,

M. Voutilainen

DepartmentofPhysics,UniversityofHelsinki,Helsinki,Finland

J. Havukainen,

J.K. Heikkilä,

T. Järvinen,

V. Karimäki,

R. Kinnunen,

T. Lampén,

K. Lassila-Perini,

S. Laurila,

S. Lehti,

T. Lindén,

P. Luukka,

T. Mäenpää,

H. Siikonen,

E. Tuominen,

J. Tuominiemi

HelsinkiInstituteofPhysics,Helsinki,Finland

T. Tuuva

LappeenrantaUniversityofTechnology,Lappeenranta,Finland

M. Besancon,

F. Couderc,

M. Dejardin,

D. Denegri,

J.L. Faure,

F. Ferri,

S. Ganjour,

A. Givernaud,

P. Gras,

G. Hamel de Monchenault,

P. Jarry,

C. Leloup,

E. Locci,

J. Malcles,

G. Negro,

J. Rander,

A. Rosowsky,

M.Ö. Sahin,

M. Titov

IRFU,CEA,UniversitéParis-Saclay,Gif-sur-Yvette,France

A. Abdulsalam

11

,

C. Amendola,

I. Antropov,

F. Beaudette,

P. Busson,

C. Charlot,

R. Granier de Cassagnac,

I. Kucher,

S. Lisniak,

A. Lobanov,

J. Martin Blanco,

M. Nguyen,

C. Ochando,

G. Ortona,

P. Pigard,

R. Salerno,

J.B. Sauvan,

Y. Sirois,

A.G. Stahl Leiton,

A. Zabi,

A. Zghiche

LaboratoireLeprince-Ringuet,Ecolepolytechnique,CNRS/IN2P3,UniversitéParis-Saclay,Palaiseau,France

J.-L. Agram

12

,

J. Andrea,

D. Bloch,

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E.C. Chabert,

V. Cherepanov,

C. Collard,

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,

J.-C. Fontaine

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,

D. Gelé,

U. Goerlach,

M. Jansová,

A.-C. Le Bihan,

N. Tonon,

P. Van Hove

UniversitédeStrasbourg,CNRS,IPHCUMR7178,F-67000Strasbourg,France

S. Gadrat

CentredeCalculdel’InstitutNationaldePhysiqueNucleaireetdePhysiquedesParticules,CNRS/IN2P3,Villeurbanne,France

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13

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UniversitédeLyon,UniversitéClaudeBernardLyon1,CNRS–IN2P3,InstitutdePhysiqueNucléairedeLyon,Villeurbanne,France

A. Khvedelidze

7

GeorgianTechnicalUniversity,Tbilisi,Georgia

Z. Tsamalaidze

7